This is a revised proposal for a Mentored Research Scientist Development Award in Aging for Dr. James D. Fluckey. This human research proposal will allow Dr. Fluckey to expand on his previous work in aging and muscle protein synthesis that was done in rats. Drs. William J. Evans and G. Lynis Dohm will serve as Co-Mentors for this project. Generally, there appears to be a decline of muscle mass and protein synthesis with advancing age, but the underlying cellular mechanisms that regulate reductions of protein synthesis are unclear. The first aim of this proposal will be to examine rates of muscle protein synthesis in younger, middle-aged and older individuals (20-80 years old), in vitro. Our hypothesis is that muscle protein synthesis, as measured in vitro, will be lower in older (60-80 y) versus middle-aged (40-59 y) or younger (20-39 y) individuals (01der<middle- aged<younger), and that the age-related decline in protein synthesis will be associated with an attenuated translational efficiency, (i.e., an impaired ability to translate available mRNA). We will examine muscle polysome density and RNA (ribosomal) content for a measure of translational efficiency (rates of synthesis per unit of RNA). The second aim of this proposal will be to better understand the signaling mechanisms associated with protein synthesis, as well as how they may be affected by age. Two major possibilities for age- related changes in protein synthesis may involve the translation machinery pre se, or with capacity to activate the machinery via signaling mechanisms. Our hypothesis is that an age-related alteration of muscle protein synthesis is a result of altered signal transduction. To test these hypotheses, we will examine rates of protein synthesis and translational efficiency in vitro from abdominal muscle strips obtained from patients undergoing laparoscopic surgery. These in vitro studies will be conducted with or without insulin (specific aim 1), a potent anabolic hormone that has been shown to influence muscle protein synthesis in rats during conditions of muscle atrophy, and with or without specific inhibitors of key signal transduction proteins (specific aim 2). Together, these studies will significantly enhance our understanding of the changes in muscle protein metabolism in senescent muscle and the mechanisms associated with these changes. The proposed studies, mentors, co- investigators, and institutional commitment at the University of Arkansas for Medical Sciences provide an outstanding environment for Dr. Fluckey to develop into an independent research scientist in aging.